It is the circle of the bears cause of ursa major and ursa minor, and the circle without bears cause ya'know opposite part of the sky.

its probably just a critters burrow.

the reason theres suction is because wind is blowing accross the other entrances and drawing air through. this how animal burrows avoid becoming co2 death traps while keeping cool. you still shouldn’t mess with it because like, thats a wild animals home and you dont know whats in it or how territorial it might be but the ground isnt going to eat you like an 80s Saturday morning cartoon. even if the burrow does cave in under you, they dont tend to be large enough for one collapsed tunnel to do more than mildly inconvenience your average adult.

anyways heres a fun diagram i found that explains this using prairie dog burrows as an example: